(1) Field of the Invention
This invention relates to an optical cross-connect apparatus and, more particularly, to an optical cross-connect apparatus for performing optical cross-connection of wavelength division multiplex (WDM) signals.
(2) Description of the Related Art
Optical communication networks form the nuclei of telecommunication networks and are expected to provide more advanced services in a wider area. In particular, WDM which is central to optical transmission systems has advanced swiftly. WDM multiplexes a plurality of optical signals with different wavelengths into a single optical fiber.
On the other hand, to build immense photonic networks, WDM systems are connected to one another to form ring networks where each node is connected in a circle, mesh networks where nodes connected form the shape of a mesh, and the like. One of key technologies for building such networks is optical cross-connect (OXC) apparatus.
OXC apparatus are installed in nodes on networks for performing switching to output an optical signal inputted to an input port to a target output port or for adding or dropping an optical signal. Usually large-scale spatial optical matrix switches including microelectro-mechanical systems (MEMSes) are used in the switching sections of OXC apparatus. Development of OXC apparatus which can switch about 1,000 channels is proceeding.
With conventional OXC apparatus, wavelength conversion is performed by a wavelength converter (transponder). In this case, a WDM optical signal transmitted is separated by an optical demultiplexer. Then obtained optical signals are converted to electrical signals and are converted to optical signals again. That is to say, optical-electrical-optical (OEO) conversion is performed. These optical signals are inputted to an optical matrix switch and are switched. Then the optical signals are wavelength-converted again by a transponder, are combined by an optical multiplexer, and are transmitted to the next stage as a WDM signal (see, for example, Japanese Unexamined Patent Publication No. 2000-134649, paragraph nos. [0020]–[0037] and FIG. 1).
With the conventional OXC apparatus, however, optical switching is realized by an optical matrix switch made up of switch cells in which micro electromechanical parts, such as MEMSes, are used, so the maximum number of channels handled is about 1,000 due to difficulty in fabricating highly integrated optical switching elements, the complexity of control, etc. A 1000.times.1000 channel switch has a throughput of 10 Tbits/s at most.
Accordingly, the conventional OXC apparatus cannot perform the switching of more than 1,000 channels, so the development of next-generation multimedia networks cannot be expected.